Purdy much what Nachos said. I mean, if someone's stealing a story wholesale, as in basically doing a find replace sort of thing with someone else's story, than that's a whole different kettle of fish whether it's fanfiction or not, but if it's just fanfiction of fanfiction? I don't see why fanfiction should get more precedence for protection than the very thing it was written from. Hell, unless it's terrible or troll fic, getting fanworks might actually be sort of a good sign, since it shows something about the work interests people enough to even write fanfiction of the fanfiction.
In other words, I echo Nachos on this one. There's far far far worse things in fanfiction than that.
For instance, completely and utterly changing so much that it hardly resembles the source material, with the characters not really resembling themselves either. I mean, there's AU, and then there's butchering the source material completely. I think that's one of the reasons High School AUs are so despised besides being so obnoxiously common and an excuse for the worse of shipping tropes, really, for doing both of these things. It's OK to take a different spin on things, that's why fanfiction exists after all, but at the same time, at least have respect for the source material, good god.
...probably all y'all are thinking of what I'm pointing at primarily here, but let's generally try to keep that to a minimum. There's been a touch too much drama here about said subject already, after all.